1. Field of the Invention
The present invention relates to a magnetic recording medium and a magnetic recording apparatus using the same. In particular, the present invention relates to a magnetic recording medium in which thermal fluctuation is suppressed.
2. Description of the Prior Art
In recent years, the recording density of HDDs (hard disk drives) has increased significantly, and recording bits recorded in a magnetic recording medium become increasingly smaller year after year. With this trend, the magnetic grain size of the recording medium becomes smaller, which causes the problem of thermal fluctuation. A criterion for determining the stability against thermal fluctuation is KuV/kBT, where Ku is the magnetic anisotropic energy of a magnetic medium, V is the volume of a magnetic grain, kB is the Boltzmann""s constant, and T is the absolute temperature. HDDs having larger KuV/kBT are more stable against thermal fluctuation. In order to solve this problem, there are two approaches: increasing Ku and increasing V by using a perpendicularly magnetized medium to increase the thickness of the film. Another attempt to improve thermal fluctuation is made by increasing the effective volume V by combining a recording medium and an antiferromagnetic film made of an oxide, NiO or an alloy such as NiMn, RhMn, CrMnPt or the like as used for spin-valve magnetic heads (JP 11(1999)-296832A).
However, when Ku is increased, the coercive force of the recording medium is increased, which makes recording by a magnetic head difficult. In order to solve this problem, it is necessary to develop a soft magnetic film having a high saturation magnetization, but there are no soft magnetic films having a 2.5 T or more at present, so that this approach will lose its effectiveness sooner or later. On the other hand, the approach of using a perpendicular magnetic recording medium theoretically can be excellent. However, in practice, there are problems such as medium noise and delayed development of magnetic heads suitable for a perpendicular recording medium. Therefore, a magnetic recording medium that has more excellent characteristics than those of a conventional inplane medium is not available yet.
Furthermore, when an antiferromagnetic film made of an oxide, NiO or the above-mentioned alloys is exchange-coupled to a recording medium, the magnetization curve of the recording medium becomes asymmetric because of the unidirectional anisotropy of the antiferromagnetic materials. When the magnetization curve of the recording medium is asymmetric, the medium is magnetized easily by an external magnetic field from one direction, whereas the medium is not magnetized easily by an external magnetic field from the other direction, and thus the stability against thermal fluctuation of a recording medium depends on the direction from which the recording medium is magnetized.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a novel magnetic recording medium in which thermal fluctuation is suppressed and a magnetic recording apparatus using the same.
A magnetic recording medium of the present invention includes a magnetic film for signal recording; and a film containing M2Oy as a main component that is magnetically exchange-coupled to the magnetic film, in order to increase the effective V and Ku of the magnetic film and thus suppress thermal fluctuation.
Herein, M is at least one element selected from Fe, Co, Ni, alkaline earth elements, Y, lanthanoids, and Bi and includes at least one selected from Fe, Co and Ni as an essential element (in other words, M is an element including at least one selected from Fe, Co and Ni, and may further include at least one element selected from alkaline earth elements, Y, lanthanoids, and Bi), and y is a value satisfying 2.8 less than y less than 3.2. In this specification, xe2x80x9cmain componentxe2x80x9d refers to a component making up 50 wt % or more.
Furthermore, a magnetic recording apparatus of the present invention includes the above-described magnetic recording medium and a magnetic head for recording information on the medium.
As described above, according to the present invention, a magnetic recording medium that is stable against thermal fluctuation even if micro signal recording is performed, and a high density magnetic recording apparatus using the same can be provided.